Time sequence of action of estrone on 3H-cytidine incorporation in the uterus and blastocyst during delayed implantation in the rat

The time sequence of action of estrone on the incorporation of 3H-cytidine in the uterus and blastocyst during delayed implantation in the rat was studied autoradiographically. When 3H-cytidine was injected into uterine horn directly during early stages of pseudopregnancy, the RNA precursor incorporation in uterine epithelium on day 1 of pseudopregnancy demonstrated a minimal number of grains in the nuclei. A large number of grains were seen over the nuclei of uterine epithelial cells on day 3 of pseudopregnancy. Heavy uptake was seen over the nuclei of uterine epithelial cells on days 4 and 5 of pseudopregnancy. When 1 μg estrone was administered to animals on day 8 of delayed implantation, estrogen enhanced the synthesis of RNA in the uterine epithelial cells at 12 hr after injection. The uptake of 3H-cytidine was seen in the nucleus as well as in the cytoplasm. RNA synthesis increased in the uterus at 12 hr and declined by 24 hr. The 3H-cytidine uptake was predominantly located in the nuclei. Estrogen caused enhanced RNA synthesis in the blastocyst at 12 hr after estrone administration. 3H-cytidine incorporation was predominantly seen in the nuclei of trophoblast cells. It has been shown that estrogen has a similar time sequence of action on the uterus and blastocyst. (author)